Round #795

Pivot a table of monthly_sales (month, year, total) to columns per month.

```csharp using System; using System.Collections.Generic; using System.Linq; public class MonthlySales { public string Month { get; set; } public int Year { get; set; } public int Total { get; set; } } class Program { static void Main() { var monthlySales = new List<MonthlySales> { new MonthlySales { Month = "Jan", Year = 2022, Total = 100 }, new MonthlySales { Month = "Feb", Year = 2022, Total = 150 }, new MonthlySales { Month = "Mar", Year = 2022, Total = 120 }, new MonthlySales { Month = "Jan", Year = 2023, Total = 130 }, new MonthlySales { Month = "Feb", Year = 2023, Total = 160 }, new MonthlySales { Month = "Mar", Year = 2023, Total = 140 }, }; var pivotedSales = monthlySales.GroupBy(s => s.Year) .Select(g => new { Year = g.Key, Jan = g.Where(s => s.Month == "Jan").Select(s => s.Total).FirstOrDefault(), Feb = g.Where(s => s.Month == "Feb").Select(s => s.Total).FirstOrDefault(), Mar = g.Where(s => s.Month == "Mar").Select(s => s.Total).FirstOrDefault(), }); foreach (var sale in pivotedSales) { Console.WriteLine($"Year: {sale.Year}, Jan: {sale.Jan}, Feb: {sale.Feb}, Mar: {sale.Mar}"); } } } ```

```csharp using System; using System.Data; using System.Linq; public class SalesPivot { public static DataTable PivotMonthlySales(DataTable monthlySales) { // Check if input table is empty if (monthlySales.Rows.Count == 0) { throw new ArgumentException("Input table is empty"); } // Get unique years var years = monthlySales.AsEnumerable().Select(r => r.Field<int>("year")).Distinct(); // Create a new DataTable with pivoted columns DataTable pivotedTable = new DataTable(); pivotedTable.Columns.Add("year"); // Add month columns for (int month = 1; month <= 12; month++) { pivotedTable.Columns.Add($"Month {month}"); } // Populate the pivoted table foreach (var year in years) { DataRow newRow = pivotedTable.NewRow(); newRow["year"] = year; var yearSales = monthlySales.AsEnumerable().Where(r => r.Field<int>("year") == year); for (int month = 1; month <= 12; month++) { var monthSales = yearSales.FirstOrDefault(r => r.Field<int>("month") == month); newRow[$"Month {month}"] = monthSales != null ? monthSales["total"] : DBNull.Value; } pivotedTable.Rows.Add(newRow); } return pivotedTable; } public static void Main() { // Example usage DataTable monthlySales = new DataTable(); monthlySales.Columns.Add("month", typeof(int)); monthlySales.Columns.Add("year", typeof(int)); monthlySales.Columns.Add("total", typeof(int)); monthlySales.Rows.Add(1, 2022, 100); monthlySales.Rows.Add(2, 2022, 120); monthlySales.Rows.Add(1, 2023, 150); monthlySales.Rows.Add(2, 2023, 180); DataTable pivotedTable = PivotMonthlySales(monthlySales); // Print the pivoted table foreach (DataRow row in pivotedTable.Rows) { foreach (DataColumn column in pivotedTable.Columns) { Console.Write(row[column] + " "); } Console.WriteLine(); } } } ```